55378-90-0Relevant academic research and scientific papers
Peptide synthesis with benzisoxazolium salts-II. Activation chemistry of 2-ethyl-7-hydroxybenzisoxazolium fluroborate; Coupling chemistry of 3-acyloxy-2-hydroxy-N-ethylbenzamides
Kemp,Wang, S-W.,Rebek Jr.,Mollan,Banquer,Subramanyam
, p. 3955 - 3967 (1974)
Mechanistic aspects of the application of 2-ethyl-7-hydroxybenzisoxazolium fluoroborate, 1, to peptide synthesis are presented. Optimal conditions are described for the formation of 3-acyloxy-2-hydroxy-N-ethylbenzamides, 2, from 1 and peptide acids. Amines are found to react with esters, 2, as their 2-oxyanion conjugate bases. Racemization in model systems is found to occur via oxazolones, and the low racemizing tendency of the esters, 2, is shown to result from a unique internal buffering effect. In the preceding paper,1 we have outlined the reasoning which led us to synthesize the 2-ethyl-7-hydroxybenzisoxazolium cation, 1, and the evidence which establishes the active esters, 2, as products of the reactions of 1 with carboxylic acid anions. In the following paper,2 we report results of the application of this reaction to the synthesis of simple amino acid derivatives. In this paper, we describe the known practical features of the activation sequence 1→2, carried out with the model, carbobenzoxyglycine, and salient features of the coupling sequence, 2→amide, carried out with a variety of peptide derivatives. Evidence relevant to the mechanisms of coupling and racemization for the esters 2 is described.
